Japanese Published Patent Application No. 7-43177 describes a position encoder designed as a rotary transducer for an electric drive. Besides position-detection means for determining the position of two drive parts, which are movable relatively to one another, the rotary transducer also includes a temperature sensor. The temperature sensor, the design of which is not described in detail, is used to measure the temperature in the housing of the rotary transducer. From this temperature, in conjunction with a preceding reference and/or calibration measurement taken during the actual measuring operation, the drive temperature of interest is inferred. From the temperature estimated in this manner in the drive area, information can be derived regarding a possible overheating of the drive windings and, if indicated, regarding temperature-related problems in the drive area. The disadvantage is, however, that ultimately there is no direct measuring information with respect to the temperature at certain parts of the drive. Accordingly, the temperature information obtained in this manner is assessed as being relatively imprecise.
Besides this variant for determining temperatures in the electric drive area, it is also conventional to position temperature sensors on the drive side which supply measuring information regarding the instantaneous temperatures in the drive area. The temperature sensors used for this purpose are usually designed as semiconductor sensors which are directly integrated in the drive windings. The drawback is that the placement of such temperature sensors necessitates an intervention in the particular drive.
Similar problems arise not only when rotary position encoders are used in combination with drives, but fundamentally when position encoders are used to measure the position of two objects which are movable relatively to one another, and a temperature sensing at one of the two movable objects is required.